Ciguatera, which is the primary and most important human-health manifestation of harmful algal blooms (HAB) and the most commonly reported marine toxin disease in the world, results from the consumption of certain fish having high levels of ciguatoxins, produced by the benthic dinoflagellate, Gambierdiscus toxicus. Despite the widespread occurrence of ciguatera in the Pacific Ocean, western Indian Ocean and Caribbean Sea, the ecology and nutrient profile of the dinoflagellate, G. toxicus, as well as the biochemical pathways involved in the synthesis of the ciguatoxin structural polyether congeners, are poorly understood. The objectives of the proposed research are to study the nutrient profile and ecology of the ciguatoxin-producing benthic dinoflagellate, G. toxicus, and to develop improved methods for detecting ciguatoxins in fish and humans. The central hypotheses are that certain nutrient conditions favor HAB and that chronic low-level exposure to ciguatoxins and its congeners results in chronic health problems. The proposed five-year study will test our hypotheses by pursuing the following specific aims: 1. Determine the nutrient profile and ecology of Gambierdiscus toxicus in Hawai'ian coastal waters. 2. Develop broadly applicable rapid-detection methods for ciguatoxins in fish. 3. Develop methods for measuring low concentrations of ciguatoxins in human sera, with the expectation of determining that low-level exposure to such polyethers is associated with chronic health problems. The proposed trans-disciplinary research is innovative, because it will provide new knowledge about the nutrient profile and ecology of G. toxicus. The proposed research represents a multidisciplinary study of an important aspect of HAB that can only be addressed by an institution, like the University of Hawai'i (UH), with internationally known researchers in the ocean and biomedical sciences and ready access to the tropical Asia-Pacific region. Overall, the newfound knowledge from this project will have a significant impact on improving prevention strategies for ciguatera fish poisoning and lead to the development of improved rapid-detection methods for ciguatoxins and its congeners in fish and humans.